Ester-substituted diaryl carbonates such as bismethylsalicylcarbonate (BMSC) have proven to be useful starting materials in the preparation of polycarbonates via the melt reaction of a diaryl carbonate with dihydroxy compounds. See for example, U.S. Pat. No. 4,323,668 in which rates of polymerization of BMSC with bisphenol A were shown to be higher than the corresponding rates of polymerization of bisphenol A with an unsubstituted diaryl carbonate, such as diphenyl carbonate. The product polycarbonate formed using ester-substituted carbonates, such as BMSC, contain high amounts of reaction byproducts such as ester-substituted phenols (e.g. methyl salicylate (MS)), inter alia, that are often removed prior to achieving a finished polycarbonate product. In order to achieve high efficiencies and to decrease amounts of unusable waste byproducts generated by polycarbonate production facilities, it would be desirable to find a use for the removed byproducts. The present invention provides a method of purifying the byproduct stream and making ester-substituted diaryl carbonates using the byproduct ester-substituted phenol.